Active MRI intramyocardial injection catheter with a deflectable distal section

ABSTRACT

A deflectable tip catheter that is safe and effective for use in a magnetic resonance imaging environment. The deflectable tip catheter is configured such that it includes a built-in antenna, such as a loopless antenna or a loop antenna. The built-in antenna permits the deflectable tip catheter to be actively tracked and/or visualized. Depending upon the specific configuration of the deflectable tip catheter, the catheter may be tracked and/or visualized as a single unit, it may be tracked and/or visualized separate and independent of other components or instruments associated with the catheter, such as pull wires, injection needles, surgical instruments, and the like. The catheters described herein include injection type catheters and/or guidance type catheters.

RELATED APPLICATIONS

[0001] The present application relates to U.S. provisional applicationserial No. 60/444,430, filed Feb. 3, 2003, which is incorporated hereinby reference, in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to catheters that have adeflectable portion. More particularly, the present invention relates todeflectable tip catheters that can be actively visualized and/or trackedin a magnetic resonance imaging (MRI) environment.

[0004] 2. Discussion of the Related Art

[0005] Occlusive coronary artery disease results in myocardialinfarction and deleterious left ventricular remodeling. Occlusivecoronary artery disease can be treated. Treatment includes coronaryballoon angioplasty, coronary artery stenting and bypass graft surgery.However, due to the limited regenerative capacity of adultcardiomyocytes, ischemic events often result in irreversible cell injuryand concurrent myocardial dysfunction, leading to congestive heartfailure and death.

[0006] There is scientific evidence that delivering therapeutic agents,such as cells (e.g., stem cells), various genetic materials, growthfactors, and the like, directly into the infracted myocardial tissue mayhelp to restore healthy tissue and normal myocardial function.Conventional interventional cardiology procedures, including theaforementioned treatments, such as balloon angioplasty, typicallyinvolve the use of a balloon catheter to dilate the occluded artery andX-ray fluoroscopy to assist the attending cardiologist guide thecatheter. X-ray fluoroscopy, however, does not distinguish healthy frominfracted myocardial tissue, nor does it provide an anatomical image ofthe heart, where the ability to distinguish infracted tissue fromhealthy tissue within an anatomical image of the heart is of vitalimportance to the cardiologist who is attempting to precisely delivertherapeutic agents using any one of the above-identified conventionaltechniques.

[0007] There are electro-anatomical mapping systems capable of providinga functional map of the cardiac anatomy; however, these systems cannotprovide real-time images of the heart. An example, is Biosense Webster'sNOGA system, which is used in conjunction with X-ray fluoroscopy. TheNOGA system employs a catheter comprising three coils and an endocardialpotential measuring electrode located at the distal tip. During clinicaluse, three external magnets are placed at three different locations onthe patient (e.g., under the patient's back and on the right and leftside of the patient's chest). The cardiologist is then able to move thecatheter around inside the left ventricle of the patient's heart, and indoing so, the NOGA system measures the electrical activity atendocardial surface, as well as the motion and the location of thedistal tip of the catheter. The NOGA system uses these measurements tocreate a three dimensional, real-time, dynamic reconstruction of theventricle, and assess the electrical and mechanical properties of themyocardium. The electrical potential and the motion of the ventricularwall are used, in turn, to differentiate healthy, viable and completelyinfracted tissue. The primary drawback of this system is that it doesnot provide an anatomical image of the entire heart. It is thereforedifficult to know the cardiac anatomy in which the catheter tip islocated, and whether the catheter tip is apposed against the septum orthe lateral wall. In addition, this procedure associated with the NOGAsystem is lengthy and the quality of the ventricle image is highlydependent on operator skill. The NOGA system is used with

[0008] MRI is a diagnostic and imaging modality that is capable ofproviding a three-dimensional map, or image of the entire heart.furthermore, MRI offers this capability without the ionizing radiationassociated with other imaging modalities, such as X-ray fluoroscopy. MRIalso provides real-time images with excellent tissue contrast; thus, theattending cardiologist can quickly and efficiently see the entire heartand clearly differentiate healthy, viable and completely infractedtissue. Ideally, MRI should be available to cardiologists for use duringintervention therapy to accurately track and precisely guide thecatheter to regions of infracted myocardial tissue.

[0009] There are many types of injection catheters currently available;however, none are well suited for use in an MRI environment. Forexample, deflectable (i.e., steerable) tip catheters includingmulti-directional, bi-directional and uni-directional deflectablecatheters are described in U.S. Pat. Nos. 5,487,757; 6,198,974; and5,755,760, respectively. Injection catheters capable of deliveringtherapeutic agents to myocardial and other tissues are described, forexample, in U.S. Pat. Nos. 5,980,516 and 6,004,295. Still further,deflectable injection type catheters are described for example, in U.S.Pat. Nos. 6,346,099 and 6,210,362.

[0010] The various catheter designs described in the above-identifiedpatents are not, as stated, well suited for use in an MRI environmentfor both procedural reasons as well as patient safety reasons. Forinstance, these catheters have ferromagnetic components that pose asafety hazard to the patient in a magnetic field environment, as theycan cause injury to the patient, as they may move in an undesired mannerdue to the magnetic field. The ferromagnetic components can also causeimage distortions, thereby compromising the effectiveness of theprocedure. Still further, such catheters contain long metalliccomponents which can cause RF deposition in adjacent tissue and, inturn, tissue damage due to an extensive increase in temperature.

[0011] In addition, it would be difficult to track and/or visualize thelocation of the catheters described in the above-identified patents inan MRI environment. In general, there are two types of tracking in anMRI environment: active tracking and passive tracking. Active trackingis the preferred methodology. It involves incorporating a transmitand/or receive antenna into the catheter design. Because a highintensity signal is transmitted or received, active tracking providesprecise location information. An example of a catheter that can beactively tracked in an MRI environment is described in U.S. Pat. No.5,928,145. In this patent, the catheter employs a loopless antenna.Another example of a catheter that can be actively tracked in an MRIenvironment is described in U.S. Pat. No. 5,699,801. In this patent, thecatheter does not have a deflectable tip, nor is it capable ofdelivering therapeutic agents to a target location, nor is it capable ofdeploying other surgical instruments such as forceps during a biopsyprocedure.

[0012] It would be very desirable to provide attending cardiologistswith a catheter design that he or she can easily steer. In addition, itwould be desirable provide a catheter that can be effectively trackedand/or visualized in an MRI environment, a catheter that is safe andeffective when used in an MRI environment, a catheter that can be usedto effectively deliver therapeutic agents to a target location withinthe patient using an injection needle, and deploy other surgicalinstruments such as a laser, a suturing device, forceps, a cauterizationtool, and the like.

SUMMARY OF THE INVENTION

[0013] Accordingly, the present invention is directed to a deflectabletip catheter that substantially obviates the deficiencies anddisadvantages associated with the related art as set forth above. Morespecifically, the present invention is directed to a deflectable tipcatheter that can be actively tracked in an MRI environment, withoutexcessive RF deposition (i.e., local tissue heating) and the othersafety and procedural drawbacks associated with the prior related art.The present invention is also directed to a deflectable tip catheterthat can be effectively used to deliver therapeutics with an injectionneedle and deploy other surgical instruments during procedures, such asa biopsy procedure.

[0014] It should be noted that the following detailed descriptionportrays the various exemplary embodiments of the present invention asbeing particularly useful in the field of cardiology. For example, thepresent invention is portrayed as being particularly useful forinjecting and/or delivering therapeutics to cardiac tissue. However, itwill be very clear to one skilled in the art that the present inventionwill be equally useful for other medical procedures, including biopsyprocedures, as well as procedures that involve other anatomical systemssuch as the brain, liver and pancreas.

[0015] As such, one advantage of the present invention is to provide adeflectable tip catheter that can be easily and effectively visualizedand tracked in an MRI environment.

[0016] Another advantage of the present invention is to provide adeflectable tip catheter that can be employed safely when used in an MRIenvironment.

[0017] Still another advantage of the present invention is to provide adeflectable tip catheter that is effective when used in an MRIenvironment and does not, among other things, distort the image, anddoes not cause local tissue damage due to excessive RF deposition alongthe length of the catheter.

[0018] Thus, in accordance with exemplary embodiments of the presentinvention, the aforementioned and other objectives are achieved with adeflectable tip catheter for use in an MRI environment. The deflectabletip catheter comprises a deflectable tip section and an RF antenna.

[0019] In accordance with exemplary embodiments of the presentinvention, the aforementioned and other objectives are also achievedwith a bi-directional, deflectable tip guide catheter. Thebi-directional, deflectable tip guide catheter includes a deflectabletip section, a first pull wire, and a second pull wire, where the firstand second pull wires are configured to form a loop antenna.

[0020] In accordance with exemplary embodiments of the presentinvention, the aforementioned and other objectives are further achievedwith a deflectable tip catheter that includes a deflectable tip sectionand an RF antenna. In addition, the catheter includes a plurality ofdistally located, non-magnetic, inductor loop coils.

[0021] In accordance with exemplary embodiments of the presentinvention, the aforementioned and other objectives are still furtherachieved with a MRI system. The MRI system comprises an MRI scanner, adeflectable tip catheter that is configured as an RF antenna, and anelectrical connection between the deflectable tip catheter and the MRIscanner.

[0022] In accordance with exemplary embodiments of the presentinvention, the aforementioned and other objectives are also achievedthrough a magnetic resonance imaging method. The method involvesgenerating a magnetic field around at least a portion of a patient andtransmitting RF energy over a portion of the patient exposed to themagnetic field. In addition, the method involves receiving the RF energyusing an RF antenna in a deflectable tip catheter located in the patientand generating a magnetic resonance image that includes a visualizationof the deflectable tip catheter in the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, together with the detailed descriptionbelow, set forth the various aspects and embodiment of the presentinvention, wherein:

[0024]FIG. 1 is a schematic diagram of a conventional, deflectable tipinjection catheter 100;

[0025]FIG. 2 is a schematic diagram of an alternative deflectable tipsection 200 associated with a conventional deflectable tip catheter;

[0026]FIG. 3 is a schematic diagram of an active MRI trackable,deflectable tip injection catheter, in accordance with a first exemplaryembodiment of the present invention;

[0027]FIG. 4A is a schematic diagram of a catheter having anon-deflectable portion that includes multiple RF chokes, in accordancewith an alternative embodiment;

[0028]FIG. 4B is a schematic diagram illustrating an alternativedeflectable tip section for an injection catheter in accordance with analternative embodiment;

[0029]FIG. 5A is a circuit diagram of a single RF output signalmatching-tuning circuit that may be employed with a deflectable tipinjection catheter, in accordance with exemplary embodiments of thepresent invention;

[0030]FIG. 5B is a circuit diagram of a multiple RF output signalmatching-tuning circuit that may be employed with a deflectable tipinjection catheter, in accordance with exemplary embodiments of thepresent invention;

[0031]FIG. 6 is a schematic diagram of an MRI trackable, deflectable tipinjection catheter that has a pre-deflected (i.e., pre-shaped), distaldeflectable tip section, in accordance with a second exemplaryembodiment of the present invention;

[0032]FIG. 7 is a schematic diagram of an MRI trackable, deflectable tipinjection catheter that includes an endiocardial potential measuringelectrode, in accordance with a third exemplary embodiment of thepresent invention;

[0033]FIG. 8 is a circuit diagram of an interface circuit that may beused in conjunction with a deflectable tip injection catheter that hasan endocardial potential measuring electrode;

[0034]FIGS. 9A and 9B are schematic diagrams of MRI trackable,deflectable tip injection catheters that include a side or lateralopening in the deflectable tip section, in accordance with a fourthexemplary embodiment of the present invention;

[0035]FIG. 10A is a schematic diagram of an MRI trackable, deflectabletip injection catheter, in accordance with a fifth exemplary embodimentof the present invention;

[0036]FIG. 10B is a schematic diagram of an interface circuit that mightbe used in conjunction with a deflectable tip injection catheter, inaccordance with exemplary embodiments of the present invention;

[0037]FIG. 11 is a schematic diagram of a uni-directional, deflectabletip guide catheter, in accordance with a sixth exemplary embodiment ofthe present invention.;

[0038]FIG. 12 is a schematic diagram of a bi-directional, deflectabletip guide catheter 1200, in accordance with a seventh exemplaryembodiment of the present invention;

[0039]FIG. 13 is a diagram of an injection needle that can be passivelytracked in an MRI environment, for use with a deflectable tip injectioncatheter in accordance with exemplary embodiments of the presentinvention;

[0040]FIG. 14 is a diagram of an injection needle, configured as a loopantenna, capable of being actively tracked in an MRI environment,separately and independently from the catheter, in accordance withexemplary embodiments of the present invention;

[0041]FIG. 15 a diagram of an injection needle, configured as a looplessantenna, capable of being actively tracked in an MRI environment,separately and independently from the catheter, in accordance withexemplary embodiments of the present invention;

[0042]FIG. 16 a schematic diagram of a deflectable tip catheter, inaccordance with a seventh exemplary embodiment of the present invention;

[0043]FIG. 17 is a schematic diagram of a deflectable tip catheter 1700,including three, non-magnetic inductor loop coils, in accordance withexemplary embodiments of the present invention; and

[0044]FIG. 18 is a schematic diagram of an M RI system, including adeflectable tip, MRI compatible catheter, in accordance with exemplaryembodiments of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0045]FIG. 1 is a schematic diagram of a conventional injection catheter100 with a deflectable tip. As shown, the catheter 100 comprises of aproximal portion that includes a non-deflectable section 105 and ahandle 110. The catheter 100 also comprises a deflectable tip section115. The deflection mechanism involves a pull wire 120 and an anchorwire 125, where the pull wire 120 and the anchor wire 125 are connectedto each other at point A in the deflectable tip section 115, as shown.The pull wire 120 runs the length of the catheter through a lumen (notshown). The anchor wire 125 is fixed at point B where the distal end ofthe non-deflectable section 105 abuts the proximal end of thedeflectable tip section 115. During clinical use, the attendingphysician (e.g., cardiologist) may actuate the deflectable tip section115 by manipulating the deflection dial 130 on the handle 110. Thisaction causes the pull wire 120 to move in the direction of the handle,relative to the anchor wire 125. As the anchor wire 125 is fixed, themovement of the pull wire 120 causes the deflectable tip section 115 todeflect as shown, for example, by arrow C. One skilled in the art willreadily appreciate the fact that an injection needle 135 may run thelength of the catheter, parallel or essentially parallel to the pullwire 120, through a second lumen (not shown), where the needle istypically made of metal, polymer or a combination of both. Again, thedrawbacks associated with catheters, such as catheter 100, when employedin an MRI environment include image distortion, burns due toradiofrequency (RF) heat deposition, the inability to accurately trackthe position and/or location of the catheter during MRI scanning.

[0046]FIG. 2 is a schematic diagram of an alternative deflectable tipsection 200 associated with a conventional deflectable catheter. Asshown, the deflectable tip section 200 comprises a slotted, metallichypotube 205. Examples of catheters comprising a slotted deflectable tipsection can be found in U.S. Pat. Nos. 4,898,577 and 5,030,204. In FIG.2, a pull wire 210 is connected to the distal end of the slotted tube atpoint A, as shown. Moving the pull wire 210 in a proximal directioncauses the deflectable tip section 200 to deflect as indicated by arrowB. Again, it will be understood by one of ordinary skill in the art thatthe corresponding catheter may be used as a delivery device to advance atool such as an injection needle (not shown) through lumen 215 of thecatheter to carry out an injection and is described, for example in U.S.Pat. No. 6,102,887.

[0047]FIG. 3 is a schematic diagram of an active MRI tracking, injectioncatheter 300, with a deflectable tip, in accordance with a firstexemplary embodiment of the present invention. More particularly, thecatheter 300 is a single or uni-direction, deflectable tip MRI activeinjection catheter arranged as a loopless antenna with multiple cores.The catheter 300 has a proximal portion that includes a non-deflectablesection 305 and a handle 310. The catheter 300 also has a distal,deflectable tip section 315. In addition, catheter 300 includes has apull wire 320 and an anchor wire 325, where the pull wire 320 and theanchor wire 325 run through a polymeric tube 335, as shown, and wherethe anchor wire 325 is connected to the pull wire 320 at point A and isfixed at point B. In this exemplary embodiment, the anchor wire 325 is aflat wire, which limits the deflection of deflectable tip section 315 tothe direction indicated by arrow C. However, it will be readilyunderstood that the anchor wire 325 may be other than a flat wire,thereby allowing for deflection in more than the one direction indicatedby arrow C. Together, the pull wire 320 and the anchor wire 325 make upa first core. It should be noted that the anchor wire 325 can be made ofan elastic material and it may be oval, elliptical, flat, triangular,and the like, in its cross-section. The pull wire 320 too may take onother shapes in cross-section.

[0048] The catheter 300 includes a second core. In the exemplaryembodiment illustrated in FIG. 3, the second core is a needle 330 whichmay be employed to deliver therapeutic agents, as set forth above, wherethe needle 330 runs through a needle tube 340. In a preferredembodiment, the needle 330 and the pull and anchor wires 320 and 325 runthrough separate tubes. Alternatively, the needle 330 and the pull andanchor wires 320 and 325 may run through a single tube in the distal,deflectable tip section 315. In another alternative to the firstexemplary embodiment, an instrument other than or in addition to theneedle 330 may be used, such as surgical forceps, where an additionalinstrument would preferably run through a separate corresponding tube,parallel or essentially parallel to the needle tube 340 and thepolymeric tube 335.

[0049] The overall length of the catheter 300 might range fromapproximately 10 cm to approximately 200 cm, where the length of thedistal, deflectable tip section 315 may range in length from 0.5 cm to30 cm, though a length between 1 cm and 6 cm is more common. Theproximal, non-deflectable portion 305 might have a length ofapproximately 10 cm to 199 cm. These lengths are intended to beillustrative and not limiting in any way as to the present invention. Asone of skill in the art will appreciate, the length of any catheter inaccordance with the various embodiments of the present invention can andwill vary depending on the intended use and application for which thecatheter is being employed.

[0050] As shown in FIG. 3, the needle 330 and the pull wire 320 areelectrically connected, for example, at point D in the handle 310, wherethe pull wire 320 and the needle 330 together serve as the cores of aloopless antenna. The loopless catheter antenna is connected to aninterface, decoupling circuit, also referred to as an interface circuit,such as the interface circuit illustrated in FIG. 5A or 5B, via acoaxial cable 345 and BNC connector 350. The interface circuit tunes theantenna to the appropriate frequency so the catheter 300 may be activelytracked within an MRI environment. The catheter antenna and theinterface circuit is connected to the MRI scanner by a coaxial cable.The interface circuits in FIGS. 5A and 5B will be described in greaterdetail below.

[0051] The non-deflectable portion 305 of catheter 300 is covered by abraided polymeric tube 355, which acts as an RF shield for the looplessantenna. The braiding is preferably made from MRI compatible material,such as nitinol, tungsten, MP35N, copper, or other like materials.Alternatively, the non-deflectable portion 305 may be covered by ashield made from flexible MRI compatible hypotubing, where thehypotubing may be laser cut at different locations along its length, orheat-treated to modify the mechanical properties, so as to make thetubing flexible.

[0052] As stated, the proximal end of the catheter 300 includes a handle310. The handle 310 houses, among other features, a deflection dial 312.The deflection dial 312 is part of the deflection mechanism.Manipulation of the deflection dial 312 causes the pull wire 320 to moverelative to the anchor wire 325 which, in turn, causes the distal,deflectable tip section 315 to deflect under the constraint of anchorwire 325, for example, in the direction indicated by arrow C. Theinterface circuits 500 and 501 described in FIGS. 5A and 5B may belocated in the handle of the deflectable tip catheter 300, in whichcase, the catheter will be directly connected to the MRI scanner.

[0053]FIG. 4A is a schematic diagram of a catheter 450 having anon-deflectable portion that includes the added safety feature ofmultiple RF chokes, in accordance with an alternative to the firstexemplary embodiment illustrated in FIG. 1. This alternative embodimentmay be particular useful in the event the non-reflectable portion of thecatheter is excessively long, and there is added concern over heat buildup along this portion of the catheter. As shown in FIG. 4A, thenon-deflectable portion has primary shielding 451, secondary shielding452, where the secondary shielding 452 has a length that is less thanone-quarter wavelength (λ/4) and is connected to the primary shielding451 at one end. At the other end, there may be a capacitor (not shown)located between the primary shielding 451 and the secondary shielding452, or simply a stray capacitance resulting from the close proximity ofthe primary and secondary shielding, where there is a primary insulationlayer 453 between the primary and secondary shielding 451 and 452. Inaddition, the secondary shielding 452 is, as shown, discontinuous. Thereis also a secondary insulation layer 456, located radially outside thesecondary shielding 452. In a preferred embodiment, there is dual lumentubing 457 running the length of the catheter 450, where a first one ofthe lumen is for pull wire 454, and the other lumen if for a surgicalinstrument, such as a needle 455.

[0054] It will be apparent that the needle 330 can extend beyond thedistal deflectable tip 315, for example, in order to deliver or inject atherapeutic agent (e.g., cells, drugs, genetic material, otherbiological materials, and the like) into tissue during a clinicalprocedure. The mechanism for manipulating the needle 335 may include aspring mechanism (not shown) for ejecting the needle 330 tissue. Thespring mechanism may be located in the distal, deflectable tip section315 or in the handle 310. The mechanism for operating the needle 330 mayalso include a luer 360 which facilitates the attachment of a syringe(not shown) containing the therapeutic agent that is to be delivered tothe tissue.

[0055]FIG. 4B is a schematic diagram illustrating an alternative distal,deflectable tip section 316 for injection catheter 300. As shown, thecatheter 400 includes, in the distal, deflectable tip section 415, apull wire 420 and an anchor wire 425. As was the case for the embodimentillustrated in FIG. 3, the anchor wire 425 is connected to the pull wire420 at point A in the deflectable tip section 415 and fixed at a point Bwhere the proximal end of the deflectable tip section 415 meets thedistal end of the non-deflectable portion 405. The catheter 300 alsoincludes an MRI compatible (i.e., non-magnetic), insulated metallic wire465 connected to the pull wire 420 or the needle 430, where the metallicwire 465 is coiled backwards upon itself, as shown. The coiled wire 465increases the MRI signal intensity associated with the distal tip of thecatheter. Thus, the deflectable tip is more visible as compared to therest of the catheter in the MR image, making it easier for the attendingphysician to locate and track the catheter 300.

[0056]FIG. 5A is a circuit diagram of an interface circuit 500 that maybe employed if the needle 330 and the pull wire 320 are electricallyconnected or shorted at the proximal end in the handle section, asshown, for example, in FIG. 3. In a preferred embodiment,matching-tuning circuit 500 includes a balun 502, which prevents shieldcurrents induced on the connecting coaxial cable (i.e., between theinterface circuit and the scanner) from being transmitted to thecatheter 300; decoupling circuitry 504, which decouples/detunes thecatheter when the MRI scanner is transmitting RF energy, thus preventingexcessive RF deposition along the length of the catheter 300; andmatching-tuning circuitry 506, which tunes the loopless antennaassociated with catheter 300 to the operating frequency of the MRIscanner (not shown), for example, 64 MHz at 1.5 Tesla.

[0057] If the needle 330 and the pull wire 320 are electricallyconnected, there is but one RF output signal associated with theloopless antenna, as shown by the single coaxial cable 345. Thus, thematching-tuning circuit 500 has but one electrical connection throughthe BNC connector 550, where the BNC connector 550, in FIG. 5A, connectswith the BNC connector 350 in FIG. 3. The matching-tuning circuit 500also has a BNC connector 570, which is electrically connected to the MRIscanner, via a coaxial cable (not shown). As there is but one RF outputsignal, the MRI scanner cannot separately and independently track thepull wire 320 (i.e., cannot separately and independently track thecatheter, which serves as the first core of the loopless antenna) andthe needle 330 (i.e., the second core of the loopless antenna).

[0058]FIG. 5B is a circuit diagram of an interface circuit 501 that maybe employed if the needle 330 and the pull wire 320 are not electricallyconnected. As shown, matching-tuning circuit 501 has a decoupling andmatching-tuning circuit A for the pull wire 320 and a separatedecoupling and matching-tuning circuit B for the needle 330. Inaddition, the matching-tuning circuit 501 includes a BNC connector 551with multiple insulated cores or a multi-pin connector, a BNC connector571 and a BNC connector 572. BNC connector 551 contains three separateelectrical conductors: one for the needle 330, one for the pull wire 320and one that serves as a ground connection. BNC connector 571 iselectrically connected to the MRI scanner via a coaxial cable (notshown), and the electrical conductor associated with the BNC connector571 carries the output signal associated with the pull wire 320.Similarly, BNC connector 572 is electrically connected to the MRIscanner via a coaxial cable (not shown), and the electrical conductorassociated with the BNC connector 572 carries the output signalassociated with the needle 330. As there are two separate outputsignals, one for the needle 330 and one for the pull wire 320, the MRIscanner can separately and independently track the position and locationof the needle 330 and the pull wire 320. As the pull wire 320 alwaysremains inside the catheter 300, it will be understood that tracking theposition and location of the pull wire 320 equates to tracking theposition and location of the catheter 300.

[0059]FIG. 6 is a schematic diagram of an injection catheter 600 inaccordance with a second exemplary embodiment of the present invention.As shown in FIG. 6, the distal, deflectable tip section 615 ispre-shaped into a relatively small radius, so the catheter 600 can moreeasily traverse through, for example, the aortic valve without causingdamage. The catheter 600 is typically advanced into the left ventriclethrough the femoral artery and across the aortic arch through the aorticvalve. Once in the left ventricle, the attending physician canmanipulate the deflection dial 612 to deflect the tip of the catheter600. To facilitate the retraction of the catheter 600 from the leftventricle, the attending physician may straighten the distal,deflectable tip section 615, as indicated by arrow A, by manipulatingthe deflection dial 612 appropriately.

[0060]FIG. 7 is a schematic diagram of an injection catheter 700 inaccordance with a third exemplary embodiment of the present invention.In this embodiment, the catheter 700 includes an electrode 775 builtinto the distal end of the deflectable tip section 715. This electrodemay be used to measure the electrical potential of adjacent tissue(e.g., endocardial tissue). Although the catheter 700, illustrated inFIG. 7, has but one electrode, it will be apparent to those skilled inthe art that it would be feasible to employ more than a singleelectrode.

[0061]FIG. 8 is a circuit diagram of an exemplary matching-tuningcircuit 800 that may be used in conjunction with injection catheter 700illustrated in FIG. 7. As shown, matching-tuning circuit 800, likematching-tuning circuit 501 in FIG. 5B, has separate RF input leads forthe pull wire 720 and the needle 730. In addition, there is separatedecoupling and matching-tuning circuitry A and B for the pull wire 720and the needle 730. Accordingly, the MRI scanner will be able toseparately track the position and location of the catheter 700 (i.e., bytracking the position and location of the pull wire 720) and the needle730. The matching-tuning circuit 800 also includes RF blocking circuitry880. The RF blocking circuitry 880 filters out any RF componentsassociated with the electrical potential output signal. Thus, the EPsignal output will more accurately reflect the electrical potential ofthe tissue adjacent to the distal end of the deflectable tip section 715of catheter 700.

[0062] In the embodiments described above, the needle, as statedpreviously, is preferably made of MRI compatible metal, e.g., nitinol,MP35N, titanium, tantalum, gold, platinum, various non-ferromagneticalloys, and the like. In addition, the needle may be selectivelyheat-treated; for example, the distal end of the needle may be heattreated, such as the last 10 cm of the needle. By heat treating thedistal end of the needle, the distal end of the needle can be adjustedfor stiffness and made more flexible than the proximal portion of theneedle. This makes it easier for the attending physician to advance theneedle into adjacent tissue (e.g., myocardial tissue) particularly whenthe distal tip of the catheter is deflected. The needle may also becoated with a hydrophilic or hydrophobic coating on the inside and/oroutside to enhance injection rates and reduce the shear stressexperienced by cells being injected through the needle. Still further,the outer surface of the needle may be electroplated using a conductingmetal, such as gold, silver, copper or the like, to enhance the RFand/or the electrical potential signal associated with the needle.

[0063] In the embodiments described above, the injection cathetersemploy but one needle. However, it will be evident that more than oneneedle may be employed, where each would serve as a separate core forthe loopless antenna. The attending physician would, of course, have theability to advance each needle individually, where each needle maycontain a different therapeutic agent.

[0064] In each of the embodiments described above, the needle projectsthrough the distal end of the deflectable tip section of the injectioncatheter. However, FIGS. 9A and 9B are schematic diagrams of aninjection catheter 900 and an injection catheter 910, respectively, inaccordance with a fourth exemplary embodiment of the present invention,wherein the injection needle 903 and the injection needle 913 projectthrough a side or lateral opening in the deflectable tip section of thecatheter, rather than an opening in the distal end of the deflectabletip section of the catheter. But for the side or lateral needleopenings, injection catheter 900 and injection catheter 910 have thesame, or substantially the same, configuration as injection catheter 300and injection catheter 400, as illustrated in FIG. 3 and FIG. 4B,respectively. Alternatively, the injection catheter 900 and theinjection catheter 910 may contain one or more needles and have multipleneedle outlets through which the attending physician may advance aneedle, including an opening in the distal end of the deflectable tipsection 915, as well as one or more lateral openings. Similarly, needlesmay be concentrically places one inside the other and advanced by theattending physician in a telescopic fashion.

[0065] Side or lateral needle openings may be quite beneficial duringcertain procedures. For example, such a catheter as illustrated in FIG.9A or 9B may be advanced into a coronary artery. The needle may then beadvanced more easily through a side or lateral opening, in thedeflectable tip section, through the arterial wall and into the adjacentmyocardium to enable delivery of a therapeutic into the tissue. Such acatheter would also be useful in a vascular bypasss procedure.

[0066] There are many additional features associated with the catheterneedle that may be incorporated into the various embodiments of thepresent invention. For example, the catheter may have a mechanismpreferably located on or near the handle of the catheter for locking theneedle in place, releasing the needle from a locked position andcontrolling the extent of needle insertion into adjacent tissue. Forexample, it may be useful to lock the needle in a retracted position toprevent the accidental injection of a therapeutic agent.

[0067]FIG. 10A is a schematic diagram of an injection catheter 1000, inaccordance with a fifth exemplary embodiment of the present invention.In this embodiment, the needle 1030 and the pull wire 1020 serve asparallel wires of an elongated loop antenna, rather than a looplessantenna. The matching-tuning circuit for decoupling and tuning the loopantenna is shown as being located in the handle 1010 of the injectioncatheter 1000. However, the matching-tuning circuit could be externallylocated, like the previous embodiments described above.

[0068]FIG. 10B is a schematic diagram that more clearly depicts aninterface circuit 1050 that might be used in conjunction with theinjection catheter 1000. The circuit 1050 includes an electricalconnector or lead for the pull wire 1020 and the needle 1030, a seriescapacitor 1021, a series capacitor 1031, a parallel capacitor 1032 and aPIN diode 1033. There may also be a series capacitor 1034 at the distalend of the inductor loop, or there may be stray capacitance induced bythe close proximity of the two conductors and the dielectric therebetween. The parallel capacitor 1032 and the PIN diode 1033 serve as thedecoupling circuitry. It will be understood, however, that othermatching-tuning circuit configurations may be employed with the catheter1000.

[0069] The exemplary embodiments described herein below, involvedeflectable guide catheters. In general, the guide catheters covered bythese embodiments comprise a proximal, non-deflectable shaft and adistal, deflectable tip section. The distal, deflectable tip sectionpreferably includes an outer tubing and, within the outer tubing, thinwalled hypotubing, made from a superelastic MRI compatible metal/alloy,such as nitinol, MP35N, and the like. The hypotubing is slotted (i.e.,it has cut-outs) on at least one side, similar to that which isillustrated in FIG. 2. The diameter of the lumen associated with a guidecatheter is relatively large, to accommodate the one or more medicalinstruments passing there through. The slotted hypotubing providesgreater deflectability where the diameter of the distal, deflectable tipsection is, as stated, relatively large.

[0070] In accordance with the guide catheters in the exemplaryembodiments described below, the proximal, non-deflectable shaft portionis preferably covered by braided or non-braided polymeric tubing. Ifbraided tubing is used, the material will be a MRI compatible metal, forexample, nitinol, tungsten, titanium, tantalum, MP35N, or a non-metal,such as Kevlar. Moreover, these guide catheters may have an inner tubingrunning the length of the catheter, where the lumen of this inner tubingwould accommodate the aforementioned medical instruments. The innertubing will be made from a suitable, MRI compatible material that alsofacilitates the movement of the one or more medical instruments (e.g.,teflon).

[0071]FIG. 11 is a schematic diagram of a uni-directional, deflectabletip guide catheter 1100, in accordance with a sixth exemplary embodimentof the present invention. As set forth above, the deflectable tip guidecatheter 1100 includes a proximal, non-deflectable shaft 1105, a handle1110, and a distal, deflectable tip section 1115. The non-deflectableshaft 1105 is covered by braided tubing 1106, where the braided tube1106 is made from an MRI compatible material. The distal, deflectabletip section 1115 contains a slotted hypotube 1116. The distal,deflectable tip section 1115 is electrically isolated from the braid1106 by an insulating strip 1107. In addition, the guide catheter 1100includes a pull wire 1120. In the non-deflectable shaft 1105, thepullwire 1120 runs along the inside of the braided tubing 1106, within awire tube 1130, thus creating an eccentric coaxial cable. In the distal,deflectable tip section 1115, the pull wire 1120 runs along the innerwall of the slotted hypertube 1116, and is attached thereto at point A,as shown. In this sixth exemplary embodiment, the braid 1106 and thepull wire 1120 together form a loopless antenna. An interface circuit,such as the one shown in FIG. 5A, may be used to decouple and tune theloopless antenna and to provide a single RF output signal for the MRIscanner, so the catheter 1100 can be actively tracked and/or visualized.

[0072] Further regarding the guide catheter 1100, the braid 1106 and thepull wire 1120 may, alternatively, be configured so as to form anelongated loop antenna, rather than a loopless antenna. In accordancewith this alternative embodiment, the braid 1106 is electricallyconnected to the proximal end of the slotted hypotube 1116, whereas theinsulated pull wire 1120 is connected to the distal end of the slottedhypotube 1116. Both the pull wire 1120 and the braid 1106 are connectedto the core and the shielding of a coaxial cable at the proximal end ofthe catheter, for example, in the handle of the catheter, wherein aninterface circuit, such as the matching-tuning circuit shown in FIG.10B, is employed to decouple and tune the loop antenna, and to generateand forward an RF output signal to the MRI scanner so that the catheter1100 can be actively tracked and/or visualized.

[0073]FIG. 12 is a schematic diagram of a bi-directional, deflectabletip guide catheter 1200, in accordance with a seventh exemplaryembodiment of the present invention. The guide catheter 1200 issubstantially similar to the guide catheter 1100, illustrated in FIG.11, but for guide catheter 1200 has two pull wires 1220 and 1221, ratherthan one pull wire, where the pull wires 1220 and 1221 are attached tothe inner wall of the slotted hypotube 1216 at points A and B,respectively, to facilitate bi-directional deflection. In addition, thetwo pull wires 1220 and 1221 are electrically configured to form a loopantenna. Although not shown in FIG. 12, an interface circuit, such asthe matching-tuning circuit in the handle of catheter 1000, illustratedin FIG. 10, may be employed to decouple and tune the loop antenna, andto provide an RF output signal for the MRI scanner so the catheter 1200can be actively tracked and/or visualized. It will be understood,however, that the two pull wires 1220 and 1221 could be configured, inthe alternative, to form a loopless antenna.

[0074] The guide catheters 1100 and 1200, described above, can, ofcourse, be modified such that they may be employed as injectioncatheters. This may be achieved, for example, by incorporating aninjection needle into the guide catheter assembly, where the injectionneedle can be actively tracked and/or visualized by providing acorresponding, separate RF path between the needle and the MRI scannervia an interface circuit. Alternatively, the needle may also bepassively tracked.

[0075]FIG. 13 is a diagram of an injection needle 1300 that can bepassively tracked in an MRI environment. As shown, needle 1300 has aproximal, polymeric tube section 1301, a distal section 1302 and a leur1303. The distal section 1302 is made of an MRI compatible metal, and itincludes a beveled tip 1304. The leur 1303 is used to attach a syringethat may contain a therapeutic agent. The length of the needle 1300 willapproximate {fraction (1/4)} wavelength (λ), for example, 10 cm for a1.5 Tesla system). In addition, the needle 1300 may be insulated oruninsulated. Preferably, there would be some calibrated indicator on thehandle, for example, that reflects the extent to which the needle 1300is deployed in the patient tissue. The primary advantage realized by theuse of needle 1300 is that the proximal polymeric section 1301 does notgenerate any significant heat, which might otherwise pose a safetyhazard for the patient.

[0076]FIG. 14 is a diagram of an injection needle 1400 that is capableof being actively tracked, separately and independently from the guidecatheter. As shown, the needle 1400 has a proximal section, where theproximal section is covered by an inner shielding layer 1401, and wherethe inner shielding 1401 is covered by an outer insulating layer 1402.The needle 1400 also has a distal tip portion with a beveled edge 1403.The distal tip portion is made from an MRI compatible metal, and itincludes a polymeric insulating sheath. Together, the shielding layer1401, the outer insulating layer 1402 and the polymeric insulatingsheath prevent the needle 1400 from generating a significant amount ofheat, which might otherwise pose a safety hazard for the patient. Inaddition, the needle 1400 has a built-in loopless antenna, which isconnected to an interface circuit via one or more electrical leads 1404through a BNC connector 1405. It is this built-in antenna that allowsthe needle 1400 to be actively tracked and/or visualized separate andindependent of guide catheter in which the needle 1400 is contained. Itshould be noted that the needle may be coated with an insulatingpolymeric dielectric layer, e.g., polyimide, polyurethane lacquer, andthe like, on the inside.

[0077]FIG. 15 is a diagram of an injection needle 1500 that is capableof being actively tracked, separately and independently from the guidecatheter. It differs from the injection needle illustrated in FIG. 14 inthat injection needle 1500 is configured as a loop antenna, rather thana loopless antenna.

[0078] It is of particular importance to be able to track and/orvisualize the distal tip of the injection needle. Thus, the needlesdescribed above may include a thin metallic wire coiled around thedistal tip. This will increase the intensity of the RF signal associatedwith the distal tip of the needle, thereby making the distal tip of theneedle more visible under MRI.

[0079] The ability to identify and select the geometric plane in whichthe catheter lies during an MRI procedure is quite important, as itallows the attending physician to then more rapidly and preciselyidentify and prescribe image slices of interest that are associated withor intersect this plane. U.S. Pat. No. 6,687,530, which is incorporatedherein by reference, proposes a methodology for tracking the location ofindividual coils located along the length of a catheter, in threedimensional space, using MRI, and acquiring an image in or associatedwith the geometric plane defined by the location of the coils. Thistechnique then permits an attending physician to identify the geometricplane and, thereafter, select and visualize imaging slices relative tothat geometric plane. A catheter in accordance with exemplaryembodiments of the present invention will now be described for use withan MRI system that employs the capability provided by this or similarmethodologies.

[0080]FIG. 16 is a diagram of a deflectable tip catheter 1600, thatincludes three individual inductor loop coils, in accordance with aseventh exemplary embodiment of the present invention, wherein the basicstructure and design of the deflectable tip catheter 1600 may take theform of any one of the catheters described in the previous exemplaryembodiments, with the addition of a guidewire lumen. The deflectable tipcatheter 1600 has, in addition to those catheters described above, aguidewire 1601 which is made from a relatively stiff, MRI compatiblematerial. Attached to or connected to the distal tip of the guidewire1601 is an inductor loop coil 1602. The attending physician willadvanced the guidewire 1601 into the left ventricle (LV), or otheranatomical structure of interest, as shown in FIG. 16. The attendingphysician then advances the deflectable tip catheter 1600 over theguidewire 1601, where the guidewire 1601 runs through a guidewire lumen1605. There are two additional inductor loop coils 1603 and 1604 locatedat the deflectable tip section of the catheter 1600. More specifically,coil 1603 is located at the fulcrum, or point of deflection, and coil1604 is located at the distal tip of the catheter 1600.

[0081] Each of the three inductor loop coils 1602, 1603 and 1604 areelectrically connected to a corresponding coaxial cable (not shown inFIG. 16) so that the MRI system using, for example, the aforementionedsoftware, can identify the location of the three inductor loop coils1602, 1603 and 1604 in three dimensional space within the anatomicalstructure of interest, track the geometric plane through the anatomicalstructure of interest defined by the location of the three coils 1602,1603 and 1604, and generate an image slice relative to the geometricplane as specified by the attending physician. Once the attendingphysician has positioned the distal tip of deflectable catheter 1600 sothat it is pointing towards the region of interest, the physician mayadvance the injection needle into, for example, the myocardial tissue todeliver a therapeutic agent.

[0082]FIG. 17 is a schematic diagram of a deflectable tip catheter 1700,including three, non-magnetic inductor loop coils, in accordance with analternative to the seventh exemplary embodiment described above. Asshown, the three inductor loop coils 1702, 1703 and 1704 are built intothe distal, deflectable tip section 1715. Each of the inductor loopcoils 1702, 1703 and 1704 are electrically connected to a correspondingcoaxial cable, as shown, so that the MRI scanner, through, for example,software as described above, can individually identify the positionand/or location of each coil in three dimensional space and, there from,acquire an image associated with the geometric plane defined by theposition of the three coils. This information will assist the attendingphysician in guiding or steering the catheter 1700 into a desiredlocation and/or position.

[0083] These individual loop coils could be coiled circumferentiallyaround the diameter of the catheter, on the outside, or place inside thecatheter tubing. In addition, the coils may be placed inside the distaltip, or other locations, and oriented in the x, y and z planes, i.e.,orthogonal to one another. The aforementioned tracking methodology couldbe implemented to track the position and location of the coils.

[0084]FIG. 18 is a diagram of an MRI system 1800 in accordance withexemplary embodiments of the present invention. The MRI system 1800 ofFIG. 18 includes a magnetic field generator 1801, for establishing amagnetic field on the patient, and an RF source 1802 for emitting RFsignals to at least a portion of the patient disposed within themagnetic field. Of particular importance, the MRI system 1800 employs adeflectable tip, MRI compatible catheter 1803, in accordance with thepresent invention, such as any of the deflectable tip cathetersdescribed herein above. In addition, the MRI system 1800 includes aninterface circuit 1804. The specific antenna interface circuit that isemployed will, of course, depend on the deflectable tip, MRI compatiblecatheter 1803 that is employed, as set forth above. The RF signalsreceived by the antenna in the deflectable tip, MRI compatible catheter1803 and the antenna interface circuit 1804 are then amplified by thepre-amplifier 1805, and converted from analog to digital by the A/Dconverter 1806. The digital signals are then provided to the processor1807, which employs hardware and/or software, as discussed above) togenerate MRI information relating to the patient, as well as theposition and location of the deflectable tip, MRI compatible catheter1803 and, in accordance with certain embodiments described above, theposition and location of any surgical instrument or instrumentscontained in the catheter 1803 (e.g., the position and location of aninjection needle). The MRI information is then displayed in the form ofa MR image on display 1808, so that the attending physician canvisualize and more effectively steer the catheter 1803 to or within theanatomical structure of interest.

[0085] It will be apparent to those skilled in the art that variousmodifications and variations of the exemplary embodiments describedabove can be made without departing from the spirit or scope of thepresent invention. Thus, it is intended that the present invention coverthese modifications and variations provided they come within the scopeof the appended claims and the equivalents thereof.

What is claimed is:
 1. A deflectable tip catheter for use in an MRI environment comprising: a deflectable tip section; and an RF antenna.
 2. The deflectable tip catheter of claim 1 further comprising: a pull wire; and a surgical instrument, wherein said pull wire and said surgical instrument are made of a non-magnetic material and configured to form said antenna.
 3. The deflectable tip catheter of claim 2, wherein said antenna is a loop antenna.
 4. The deflectable tip catheter of claim 2, wherein said antenna is a loopless antenna.
 5. The deflectable tip catheter of claim 4, wherein said loopless antenna has multiple cores insulated from one another, and wherein the cores move with respect to each other.
 6. The deflectable tip catheter of claim 5, wherein said pull wire serves as a first core of the loopless antenna and said surgical instrument serves as a second core for the loopless antenna.
 7. The deflectable tip catheter of claim 2 further comprising: an interface circuit including at least one RF output.
 8. The deflectable tip catheter of claim 7, wherein the interface circuit includes: a first RF output corresponding to the surgical instrument; and a second RF output corresponding to the pull wire.
 9. The deflectable tip catheter of claim 2, wherein said deflectable tip section comprises: at least one opening for said surgical instrument.
 10. The deflectable tip catheter of claim 9, wherein the at least one opening for said surgical instrument is located in the distal end of the deflectable tip section.
 11. The deflectable tip catheter of claim 9, where the at least one opening for said surgical instrument is located laterally in the deflectable tip section.
 12. The deflectable tip catheter of claim 2, wherein said surgical instrument is an injection needle.
 13. The deflectable tip catheter of claim 2, wherein said surgical instrument is a forceps.
 14. The deflectable tip catheter of claim 2, wherein said deflectable tip section comprises: a non-magnetic conductor coil electrically connected to said pull wire.
 15. The deflectable tip catheter of claim 1, wherein said RF antenna is a loopless antenna comprising multiple cores that move relative to each other.
 16. The deflectable tip catheter of claim 15, where at least one core provides means for delivering therapeutics.
 17. The deflectable tip catheter of claim 15, where at least one core provides means for measuring an electrical potential.
 18. The deflectable tip catheter of claim 15, where at least one core provides means for steering the deflectable tip catheter.
 19. The deflectable tip catheter of claim 1 further comprising: a handle; and a shielded, non-deflectable section located between said handle and said deflectable tip section, wherein said deflectable tip section is pre-deflected.
 20. The deflectable tip catheter of claim 19, wherein the RF antenna is a loopless antenna including multiple cores insulated from one another, and wherein the shielded, non-deflectable section comprises a plurality of non-magnetic RF chokes connected to the shielding.
 21. The deflectable tip catheter of claim 20, wherein the RF chokes are substantially one-quarter wavelength (λ/4).
 22. The deflectable tip catheter of claim 1, wherein said catheter is a deflectable tip guide catheter, and wherein said deflectable tip section comprises a slotted hypotube.
 23. The deflectable tip catheter of claim 1, wherein said deflectable tip section comprises: an electrode for sensing the electrical potential of adjacent tissue.
 24. The deflectable tip catheter of claim 1 further comprising: an interface circuit that includes at least one RF output, RF blocking circuitry and an electrical potential output connected to the RF blocking circuitry.
 25. A bi-directional, deflectable tip guide catheter comprising: a deflectable tip section; a first pull wire; and a second pull wire, wherein said first and said second pull wires are configured to form a loop antenna.
 26. The guide catheter of claim 25 further comprising: a handle; and a shielded, non-deflectable shaft portion located between the deflectable tip section and the handle.
 27. The guide catheter of claim 25 further comprising: a lumen axially located along the length of the guide catheter, wherein the lumen is adapted to accommodate at least one surgical instrument.
 28. The guide catheter of claim 27, wherein the surgical instrument is an injection needle.
 29. The guide catheter of claim 28, wherein the injection needle comprises: a proximal, polymeric section; and a distal tip section that includes a beveled edge.
 30. The guide catheter of claim 28, wherein the injection needle comprises: an insulated, shielded proximal section; and a polymeric, insulated tip section, that includes a beveled edge, and wherein the injection needle is configured as a loopless antenna.
 31. The guide catheter of claim 28, wherein the injection needle comprises: an insulated wire, and wherein the injection needle is configured as a loop antenna.
 32. A deflectable tip catheter comprising: a deflectable tip section; an antenna; and a plurality of distally located, non-magnetic, inductor loop coils.
 33. The deflectable tip catheter of claim 32 further comprising: a guidewire; and a guidewire lumen running axially along the length of the catheter, wherein said catheter is moveable over said guidewire.
 34. The deflectable tip catheter of claim 33, wherein at least one non-magenetic, inductor loop coil is located on the guidewire.
 35. The deflectable tip catheter of claim 33, wherein at least two non-magnetic, inductor loop coils are located in the deflectable tip section of the catheter.
 36. The deflectable tip catheter of claim 32 comprising at least three non-magnetic, inductor loop coils. III-B.
 37. An MRI system comprising: an MRI scanner; a deflectable tip catheter that is configured as an RF antenna; and an electrical connection between said deflectable tip catheter and said MRI scanner.
 38. The MRI system of claim 37, wherein said electrical connection comprises: an interface circuit.
 39. The MRI system of claim 38, wherein the interface circuit is located in a handle portion of the deflectable tip catheter.
 40. The MRI system of claim 38, wherein said antenna is configured as a loopless antenna.
 41. The MRI system of claim 38, wherein said antenna is configured as a loop antenna.
 42. The MRI system of claim 37 further comprising: means for processing RF signals received from said antenna.
 43. The MRI system of claim 42 further comprising: means for tracking the deflectable tip catheter inside a patient based on the processed RF signals received from the antenna.
 44. The MRI system of claim 42 further comprising: means for visualizing the deflectable tip catheter inside the patient based on the processed RF signals received from the antenna.
 45. The MRI system of claim 42, wherein said deflectable tip catheter comprises a plurality of inductor loop coils, and wherein the processing means comprises: means for determining a location within the patient for each of the inductor loop coils; means for identifying an image slice, in three dimensional space, as a function of the location of the inductor loop coils.
 46. The MRI system of claim 42, wherein said catheter contains an injection needle, and wherein said MRI system further comprises: an electrical connection between the needle and the MRI scanner, separate and independent of said electrical connection between said deflectable tip catheter and said MRI scanner.
 47. The MRI system of claim 46, wherein the processing means comprises: means for tracking said deflectable tip catheter based on the RF signal received from the antenna; and means for tracking the needle, separate and independent of said deflectable tip catheter based on signals received by said MRI scanner over the electrical connection between the needle and the MRI scanner.
 48. A magnetic resonance imaging method comprising the steps of: generating a magnetic field around at least a portion of a patient; transmitting RF energy over a portion of the patient exposed to the magnetic field; receiving the RF energy using an RF antenna in a deflectable tip catheter located in the patient; and generating a magnetic resonance image that includes a visualization of the deflectable tip catheter in the patient.
 49. The method of claim 48 further comprising the step of: steering the deflectable tip catheter to a location of interest in the patient using the image that includes the visualization of the deflectable tip catheter.
 50. The method of claim 49, wherein the deflectable tip catheter is an injection catheter that contains an injection needle, said method further comprising the step of: injecting a therapeutic into the patient using the injection needle. 